Introduction

Note: This article has been updated to interact with Office 2007. I left the old .NET 1.0 solution for Office XP available for download for reference (in case you are using an old version of Office).

This is a short introduction to opening an existing Microsoft Excel spreadsheet using Visual C# .NET. The computer must have Excel installed on the system for this code to run properly. The Excel assembly is used to open and manipulate Excel spreadsheets.

Code Explanation

First, the Excel assembly must be added to the project. To do this you must add a reference to the Microsoft.Office.Interop.Excel library by going to the Project -> Add Reference menu item. Go to the .NET tab of the dialog box that pops up and scroll down the Microsoft.Office.Interop.Excel list item. Double click on it and press OK. This adds the reference to your project. In the "using" section of your code, type

using Excel = Microsoft.Office.Interop.Excel;

Once the assembly is added to the project, a new application needs to be created:

Excel.Application excelApp = new Excel.Application();

If you want to make Excel visible to the user you have to set the Visible property to true, the default is false.

excelApp.Visible = true;

The code above opens the Excel application, in order to use the application, you have to open a workbook by creating a Workbook object. You can open a new blank workbook by using the following code:

Excel.Workbook newWorkbook = excelApp.Workbooks.Add();

The preceding code opens a blank workbook with one sheet. The .Add method optionally takes a template object. If the parameter is left blank, the default template will be used (like when you open Excel manually).

If you want to open an existing document for editing instead of creating a new one, you can use the following code to open the Workbook object:

The preceding code may need a little explanation. The workbookPath is of course the path to the existing spreadsheet that you want to open, and if using .NET 4.0 and the Office 2007 library (Microsoft.Office.Interop.Excel library), it is the only parameter required. The rest of the excelApp.Workbooks.open parameters are a little less obvious. The following is the list of parameters that are passed to the function:

Once the workbook is either created or opened, you must create a Sheets object that holds the Worksheets within the workbook. The following code will get all of the sheets in the workbook you previously opened.

Excel.Sheets excelSheets = excelWorkbook.Worksheets;

Now that you have the collection of Worksheets, you must get an individual sheet edit data within.

In the preceding code, you have to type cast the excelSheets.get_Item(string) method because it returns an
object. Now that you have the sheet you are ready to access individual cells with the following code:

The get_Range function must take two parameters. If the two parameters are equal, a single cell is selected; otherwise a range of cells will be selected. Again you have to type cast the return value of the method. Once you have a cell object, your can set its value using the .Value2 property, or use any of the other properties to manipulate ranges of cells.

Unfortunately I am unable to re-create the problem, but here is a suggestion that will hopefully help:

In the project I supplied it has some outdated references, so try adding the new reference from the Project->Add References... menu choice. Go to the COM tab and choose the most current Microsoft Excel library. Then go to the References folder under the solutions explorer and remove the Excel and Microsoft.Office.Core references. If you get some compile errors like Excel is not a valid reference or something like that, put this into the using directives: using Excel = Microsoft.Office.Interop.Excel;

I am wondering if the the Excel and Microsoft.Office.Core references are causing some conflicts.